Modern PLDs have increased, and continue to increase, in complexity. Typical PLDs contain several tens of millions of transistors. On the one hand, the increased complexity of the PLDs has resulted in improved performance levels and increased flexibility. On the other hand, PLDs' complexity and the large number of transistors has resulted in increased power consumption in the device. As device dimensions decrease below 0.1 micron, power becomes a more critical concern. This trend will likely continue, as the complexity of PLDs increases.
One method of addressing power consumption is to reduce the supply voltage of the chip, but this technique is less attractive in a PLD because the threshold drop of the n-type metal oxide semiconductor (NMOS) pass transistors causes a relatively serious degradation in speed. It is possible to overcome this limitation by boosting the gate voltage on the pass transistors, but doing so may cost extra processing steps to provide an extra oxide thickness, as well as possibly require a charge pump to supply the extra current. A need therefore exists for optimizing power consumption of PLDs for desired performance characteristics.